This disclosure relates in general to automated location determination and, more specifically, but not by way of limitation, to determining a location of a wireless device.
There is an ever growing desire to know geographic position of various mobile devices. For example, cellular phone operators are trying to comply with requirements to locate handsets for emergency purposes. Once position is known, emergency personnel can be dispatched to aid resolving the emergency. Knowing geographic location serves many other purposes such as geographic-tied advertising, child supervision, automated parolee supervision, reverse 911, fleet vehicle tracking, etc.
Conventional location techniques have difficulty accurately resolving location in certain situations. Satellite-based location systems suffer from inaccuracies when a clear view the sky is unavailable. Terrestrial-based systems require communication with several base stations that serve as known references during trilateration, but in some scenarios, since these systems were primarily designed for communication purposes there are not enough geographically dispersed base stations within communication range of the mobile device. Even when communication is possible to multiple base stations, multi-path induced inaccuracies can degrade the ability to resolve an accurate location.
Conventional location techniques have a wireless phone interacting with base stations associated with the service to which the wireless phone is subscribed. An almanac of base stations indicates to the wireless phone where the base stations are located. On most occasions, at least couple of base stations are visible to the wireless phone.
Cellular phones often have limited memory to store additional information. Base stations are constantly being added, removed or relocated in a cellular phone network. Almanacs of base stations are occasionally sent to cellular phones to aid in determining location. To communicate and store a large almanac is impractical on some cellular phones.